Magnetic and Mössbauer study of metal‐zeolite interaction in catalysts

Molecular sieve aluminosilicates, such as ZSM‐5 and mordenite, when impregnated with highly dispersed Fe, yield catalysts for the selective conversion of coal‐derived syngas (CO+H2) to liquid hydrocarbon fuels. Fe performs the primary Fischer‐Tropsch (FT) syngas to yield light olefins which are converted by the acidic (H+) and shape‐selective function of the zeolite to high octane gasoline components. The physical aspects of the Fe‐mordenite interaction studied by magnetic measurements, Mössbauer, and IR spectroscopy are reported and correlations with the catalytic properties are drawn. Mordenite samples with [SiO2/Al2O3] ratio in the range 12 – 60 were impregnated with 15 wt. % Fe using Fe3(CO)1 2; decarbonylation yielded superparamagmetic dispersions of γ‐Fe2O3, in the range 1.4–5.0 nm; the smallest particles were obtained for a ratio=17. Hydrogen chemisorption also revealed a similar trend in Fe dispersions. No samples, other than the one with a ratio=60 and containing the largest particles could be carbided under usual conditions. The acidity of the mordenite and the aromatics fraction in liquid hydrocarbons from syngas conversion also showed maxima at a ratio=17. The presence of a strong metal‐support interaction between Fe and mordenite was thus influenced by the varying ratios in the mordenite in a manner that paralleled the acidity and catalytic activity